Process of extracting metals from their ores



w. E. GEEENAWALT. PROCESS OF EXTRACTING METALS FROMTHEIR ORES.

' APPLICATION FILED DEC. 13, 1 915. RENEWED SEPT. 15, 1919. 1,345,846.

. Patented July 6, 1920.

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WILLIAM E. GREENAWALT, OF DENVER, COLORADb.

PROCESS OF EXTRAC'IING METALS FROM THEIR ORES.

To all whom it may concern:

lie it known that I, WILLIAM E. GREENA WALT, a citizen of the UnitedStates, residing in the city and county of Denver and State of Colorado,have invented certain new and useful Improvements in Processes ofExtracting Metals from Their Ores, of which the following is aspecification.

This invention relates generally to processes ofextracting metals fromtheir ores, and more particularly to those methods involvingelectrolytic deposition of the metals extracted from the ore by solventof the metal. lts object is to render the process more efficient and toovercome, or reduce, the effect of deleterious salts in the solutionduring electrolysis.

The process will be described more particularly in its application tothe extraction of copper from its ores, to the conditions of which it iseminently adapted. although it is in no wise intended to limit it tothis use alone.

In the electrolysis of impure copper solutions, asfor example thoseobtained from leaching copper ores with a sulfate solution,

there is always present iron sulfate which injuriously affects theoperation. Ferrous sulfate in the electrolyte is not particularlyharmful, but the ferric sulfate is highly detrimental.

If a solution of copper sulfate, containing ferrous sulfate, iselectrolyzed, copper is deposited at the cathode While sulfuric acid andferric sulfate are produced at the anode, as represented by thefollowing equations:

The ferric sulfate, finding its way back to the cathode, combines withthe deposited copper and is again reduced to the ferrous condition, thusrepresenting a loss of efficiency, as represented by the equation:

if, however, the ferric sulfate can be reduced at the expense of acomparatively cheap reducing agent, such as hydrogen sulfid, coppersulfid, or sulfur dioxid, then the iron in the electrolyte loses itsability to combine with the deposited copper, while at Specification ofLetters Patent.

Patented July 6,1920.

7 Application filed December 13, 1915, Serial No. 66,621. RenewedSeptember 15, 1919. Serial No. 323,997.

the same time, an equivalent of acid is regenerated, as shown by thefollowing equations:

The present method of carrying out these reactions will now bedescribed, as applied to the treatment of copper ores.

The ore, treated raw if an oxid and roasted if a sulfid, isleached withwater or a sulfate solution, such as dilute sulfuric acid. The richcopper sulfate solution, resulting from the leaching, is electrolyzed todeposit the copper, while at the same time an equivalent of acid isregenerated. The rich copper solution will inevitably contain some ironsulfate, and in the electrolytic deposition of the copper will givetrouble. To overcome this there is introduced into the electrolyte asubstance capable of reacting with the ferric salts, by first combiningthe substance with an insoluble carrier, such as sulfur or charcoal. Tocarry this out, cop per is combined with the sulfurfand sulfur dioXidwith the charcoal.

Tf copper is combined with the sulfur, the ore after having been leachedand filtered for the rich copper solutions to be electrolyzed, is thenwashed to remove the remaining soluble copper, which results in a leancopper solution. This lean copper sulfate solution cannot be effectivelyelectrolyzed and is precipitated in some other way. For the purpose ofthis process the lean, or very foul, copper solutions, which cannot beeffectively electrolyzed are treated with hydrogen sulfid, when thecopper in the solution combines with the sulfur of the hydrogen sulfidto form'copper sulfid. This copper sulfid is finely divided, and whenfiltered from the solution is in a comparatively pure and concentratedform, and in an ideal condition to react with the ferric salts in theelectrolysis of the rich solutions. This cop per sulfid is then appliedto the electrolyte, or rich copper solutions, to react with the variablevalent compounds, such as the ferric salts. The method of applying itwill be described later.

If sulfur dioxid is to be used, either alone or in connection with thecopper sulfid, it cannot be effectively applied in its gaseouscondition, for, the gas, per se, is only slightly soluble in water andthe reaction with the variable valent salts is slow. To more effectivelyapply it,'it 1s first combined with finely pulverized charcoal.-

v the chemical industry. ,The'charcoal, heavily charged with sulfurdioxid, can then be applied to the electrolyte, or rich coppersolutions, with no perceptible liberation of the free gas. In this waythe gas may be brought in intimate and effective contact with thevariable valent elements, while the charcoal remains unaffected and maybe re used as often as desired.

.In applying the copper sulfid, or sulfurdioxid and charcoal, to theelectrolyte, or rich copper solutions, an apparatus such as shown in theaccompanying drawings is preferred. .In these drawings Figure 1represents a cross section of an electrolyzer; Fig. 2 partlongitudinalsection and elevationyFigs. 3 and 4 a detail elevation and section ofthe diaphragm; Fig. 5 a detail section of the bottom of theelectrolyzer, and Fig. 6 a detail section of cathodes.

In the drawings, 1 represents an electrolytic tank, 2 the diaphragms, 3the anode, 4 the cathodes, 5 a pipe having perforations 6 by means ofwhich air or other gas is introduced into the anode compartment of theelectrolyzer and is regulated by the valve 7. 8 and 9 representrespectively the pipes by means of which the electrolyte is introducedinto the anode and cathode compartments of the electrolyzer, and 10 and11, respectively the pipes through which the electrolyte is withdrawn. V

A suitable diaphragm is somewhat difiicult of construction. A preferredarrangement is that shown in the drawings, in which the diaphragm iscomposed of suitable porous slabs 2, assembled and held in place by ametal rod 12 fitted in the grooved joints 14: of the porous slabs, andprotected from the action of the electric current'and the corrosiveelectrolyte by the rubber tubing or covering 13. This stiffening andsupporting rod is very conveniently'made by inserting a metal rod intohard rubber tubing and cementing it in position. The metal will give thedesired stiffness and strength while the rubber will give the desiredinsulating and acid resisting qualities. In this way a diaphragm may beconstructed which will resist the action of the current and the solutionindefinitely.

' The anodes 3 may preferably be made of lead or carbon, and fixed inposition by the sumed as being a lead cathode surrounded.

by a perforated franfe 15, in which the perforations are shown by 16;the cathode and surrounding frame are fixed in position by the strips18. The object of thisarrangement is to give uniformity to the catholyteand make it possible to use permanent lead sheets for the cathodes. Theedges of the cathode are embedded in the surrounding frame and therebyinsulated, so that no deposition of copper will take place on the edges.This cathode sheet may be made, say of one quarter inch thick hardantimonial lead. When the copper has been deposited on this cathodesheet of the desired thickmess, the cathode and frame are removed fromthe tank together, the frame removed from the edges, and the copperremoved from the face of the sheet. This avoids the necessity ofstarting sheets, and ischeaper and more convenient. i

In the operation of the process, the concentrated copp'er sulfidprecipitate obtained *from the weak and extremely foul solutions,

as already described, is introduced into the anode compartment of theelectrolyzer, while the rich copper solutions are introduced into the acathode compartment. When the current is turned'on copper-is depositedon the cathode while sulfuric acid and ferric sulfate are produced inthe anode. The electrolyte in the anode compartment is preferablyagitated, as with compressed air introduced through the perforated pipe5: this reduces the voltage required in the process and makes thedepolarization more effective. Any attempt of the ferric salts to get tothe cathode is frustrated by the reaction shown in equation 5, if coppersulfid is used, and by the reaction shown in equation 6 if sulfur dioXidcombined with charcoal is used.

In this way a high current efficiency is obtained in the deposition ofthe copper and in the regeneration of the solvent, while the operationis practically unaffected by the amount of iron in the electrolyte. Atight of any reasonable size Bil till

rsaaeac diaphragm is not essential to successful operation: thediaphragm acts largely to keep the insoluble reducing agent in the anodecompartment from getting to the cathode, so that even if some of thereduced solution from the anode compartment gets into the cathodecompartment no perceptible harm will be done. Tt is preferred tocirculate the electrolyte in the two compartments separately, althoughthis is not necessary. The sulfid sludge in the anode compartment willnot need much circulation, and will be required only as the elementalsulfur, or charcoal, shown by equations 5 and 6 becomes excessive.

This method of procedure, serves two important purposes: The leansolutions which could not be advantageously treated electrolytically aretaken care of chemically, while the resulting copper sulfid is used tomake effective the electrolytic treatment of the rich solutions, andallthe copper is in the end converted into the pure electrolytic metalby the process in its regular working. The copper sulfid, asprecipitated from the lean solutions, is light, highly effective, and iseasily maintained in suspension as a sludge in the anode compartment, asdisclosed in theBprcferred method of operation. rouri ding the cathode auniform supply of electrolyte at the surface of the cathode is assured.

The electrolyte in the cathode may also be agitated, but this is notessential, as the copper is never very closely extracted from theelectrolyte, and the regular circulation of the comparatively richsolution will bring the copper ions in suiiicient contact with thecathode to obtain a high etliciency.

This application may he considered as a continuation in part of mycop-ending application, SerialNo. 15,583, filed March 19, 1915.

T claim:

1. A process of extracting copper from its ores which consists intreating the ore with an acid solution to dissolve the copper,separating the rich copper solution from the gangue, washing the residueand thus obtaining a lean copper solution, electrolyzing the solutionrich in copper to deposit the metal and regenerate acid, precipitatingthe lean copper solution with hydrogen sullid means of the perforatedframe surand thus obtaining copper sulfld precipitate from the leancopper solutions, and then applying the copper sulfid precipitate to theelectrolyte to reduce the variable valent salts in the electrolyte totheir lowest valencg.

2. process ofextracting copper from its ores which consists in treatingthe ore with an acid solution to dissolve the copper, electrolyzing aportion of the dissolved copper to deposit the metal and regenerate theacid combined with the copper, precipitating some of the copper as thesulfid with hydrogen sulfid, filtering the sulfid precipitate from theprecipitated solution, adding the sulfid precipitate sludge to theanolyte of the electrolyte, and agitating the copper sulfid sludge incontact with the anode while maintaining it separate from the cathode.

3. A process of extracting copper from its ores which consists intreating the ore with an acid solution to extract the copper, separatingthe rich copper solution from the gangue, washing the residue and thusobtaining a lean copper solution, electrolyzing the rich copper solutionto deposit the metal and regenerate the combined acid, precipitating thelean copper solution with hydro gen 'sulfid and thus obtaining a coppersul fid precipitate from the lean solutions, and then applying thecopper sulfid precipitate to the rich solutions to reduce the ferricsalts to the ferrous salts produced by the electrolysis or the richcopper solutions.

4:. A process of extracting copper: from its ores which consists intreating the ore with a dilute acid solution to dissolve the copper,separating the resulting impure rich copper solution containing salts ofiron from the gangue, washing the residue and thus obtaining a leancopper solution, electrolyzing the rich copper solution to deposit thecopper with the simultaneous regeneration of acid and the production offerric salts, chemically precipitating the copper from the leansolution, and then applying the chemical precipitate to the rich coppersolution to reduce the ferric salts produced by the electrolysis from ahigher to a lower valency.

VVTLLTAM GBEENAWALT. fitnesses Faun L. Scorn, Conn snnawam.

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